The present invention relates generally to the field of automated monitoring of swimming pools, and the like, to detect possible drowning victims. More specifically, the invention relates to systems which use only sensors that are above the water line, to alert responsible persons monitoring a pool of water, by detecting behaviors consistent with those of someone who is unconscious or otherwise incapacitated.
Devices for automated monitoring of swimming pools have been known in the prior art. Such devices have employed video or other sensor technologies, such as sonar. Examples of such devices are given in U.S. Pat. Nos. 6,133,838, 7,330,123, and 5,043,705, the disclosures of which are incorporated by reference herein.
The above-described prior-art devices are limited in their functionality, in that all require the mounting of sensors below the surface of the water. Mounting the sensors below the surface requires a more costly and disruptive installation procedure, requiring the routing of power and data wires underwater, or through the pool walls, back to the sensor processing hardware. Also, the systems of the prior art require extensive or cumbersome calibration methods or algorithms to reduce false alarm rates.
In U.S. Pat. No. 6,133,838, there is described a system using underwater cameras mounted to the walls of a swimming pool. Underwater cameras have an advantage in seeing underwater objects and humans without the obscurations caused by the surface refraction effects at the air-water interface. However, the use of such a system involves the cost and complications of draining the pool, drilling large holes into the pool wall, installing watertight video camera housings, and excavating behind the wall to route wires to the cameras.
Moreover, in the above-described system, because the underwater cameras must be flush with the wall contours, the system has blind spots immediately adjacent to the pool walls, especially near the cameras. The prior art system must accept these disadvantages as the price for avoiding the additional signal processing needed to extract useful images if the cameras were mounted above the water surface.
U.S. Pat. No. 7,330,123 discloses sonar devices mounted underwater on the pool walls, and/or the pool bottom, to scan for objects and humans displaying characteristics of interest. These are active sensors, as contrasted with the passive sensors of the present invention. Pool-mounted active sensors are likely to be accidentally dislodged or blocked by swimmers, thus disabling one or more of the sensors. The system also requires that a person with an active sensor be in the pool, to support calibration of the overall system for different numbers of swimmers and/or levels of activity.
U.S. Pat. No. 5,043,705 uses a similar active sonar system to scan the surfaces within the volume of a pool, to generate images from which the system can discern objects and humans who are stationary. As in the above-described patent, its sensors are vulnerable to accidental dislodgment and/or blockage by swimmers.
The sonar systems of the prior art could not be mounted above the water surface. The problems of the video-based prior art could theoretically be avoided by providing sensors above the pool. However, the prior art has taught against doing so, because of the intractable problems encountered.
Specifically, the air-water boundary presents a number of challenges to sensing algorithms and makes it impractical simply to move an underwater system to a position above the water line. A water surface has small surface waves, creating a roughened water surface, akin to a rough ocean on a small scale. This surface acts as a series of small areas with slightly different refraction properties, producing the fractured and distorted view seen when observing objects underwater. Objects appear disjointed to an observer and often are missing segments due to changes in surface refraction distorting and breaking up the sensed image of underwater objects.
Moreover, varying water quality and lighting conditions alter the sensed image of the water being monitored, adding to the difficulty of using above-pool sensors.
Sensors mounted underwater do not have to deal with glare on the surface of water, or surface refraction. Further, underwater sensors are oriented to resolve the up and down motion of swimmers, while above water sensors are usually positioned at a more oblique angle, and must use passive ranging techniques to monitor motion in the critical vertical axis. For these reasons, it is impractical simply to move an underwater system of the prior art to a position above the water line.
It is the purpose of the present invention to overcome the above problems, and to provide a practical system and method for monitoring a swimming pool from above the pool. The present invention provides a new and useful above-water pool-monitoring system which is simpler in construction, more universally usable, and more versatile in operation than the devices of the prior art.